Circuits for deriving a common output signal from a plurality of amplifiers in apparatus for detecting blemishes in sheet material

ABSTRACT

A circuit for combining the outputs of several amplifiers, through an array of diodes, so that the combined output has a noise content whose amplitude is less than that of the individual amplifier outputs. The circuit is described as part of an inspection system for detecting blemishes in sheet material flowing past a series of photo-sensitive devices, the amplifiers receiving the outputs of the photo-sensitive devices.

nlted States Patent 1191 1111 ,827,809 Nash Aug. 6, 1974 CIRCUITS FOR DERIVING A COMMON 3,128,385 4/l964 Scharf et al 250/562 OUTPUT SIGNAL FROM A PLURALITY 0 3206.606 9/ I965 Burgo et al. 356/200 X AMPLIFIERS IN APPARATUS FOR DETECTING BLEMISIIES IN SHEET MATERIAL Primary Exammer.lames W. Lawrence Assistant Examinef-T. N. Grigsby Inventor! Paul Nash, 44 WeStbOUrne en, Attorney, Agent, or FirmBrowdy and Neimark London, England [22] Filed: May 11, I973 [21] App]. No.: 359,511 57 ABSTRACT [30] Foreign Application Prioi'ity Data A circuit for combining the outputs of several amplifi- May 12, 1972 Great Britain 22393/72 through an array of diodes, so that h m ined May 19, 1972 Great Britain 23/11/72 Output has a noise content Whose amplitude is less than that of the individual amplifier outputs. The cir- 52 us. (:1. 356/200, 250/562 wit is described as part of an inspection system for 5 1m, 01 21 30 2 32 301 21 30 detecting blemishes in sheet material flowing past a 581 Field of Search 250/562; 356/200 series of photo-sensitive devices, the amplifiers receiving the outputs of the photo-sensitive devices. [56] References Cited UNITED STATES PATENTS 15 Claims, 41 Drawing Figures 3,105.152 9/]963 Nash 356/200 PATENTEnws slam sum as or 23 PATENTEU M13 6 I974 saw on or 23 PAIENIED AUG 61974 sum as or 23 PAIENHU MN; 61974 arm 01 0F 23 PATENTEDAUE 61974 sum as or 23 FIG. 6A.

PAIENIEnAm: 61874 SHEU 10 0F 23 Fla. 8. 1/07 PATENTEDAUB 51974 sum '12 or 23 PAIENTEnAus 81974 saw 13 or 23 PATENTEBAUE 6 I974 sum "1a or 2 Ill/J 18/ 'IIIIIIIJ.

PATENTEDAUB 6|974 sum 18 or 23 HHHHHHAH uNN PATENTEDAUB 3.827.809

' sum 19 or 23 iiiiu l n +H+ 0/6 m/sec 

1. Apparatus for detecting blemishes in sheet material arranged to flow past an inspection head of the apparatus, the apparatus comprising light source means arranged to direct light onto the sheet material, a plurality of photosensitive devices arranged in the inspection head in a line transverse to the direction of flow of the sheet material so that the photo-sensitive devices receive light transmitted through or reflected from respective adjacent portions of the sheet material as it passes the photo-sensitive devices, each device being adapted to generate an electrical signal dependent on the intensity of light received by the device, and a circuit for deriving a common output signal from a plurality of amplifiers each adapted to generate in response to an input signal individual to the amplifier an electrical output signal including a random noise signal, the circuit comprising a plurality of rectifiers each having one terminal adapted to be connected to the output terminal of one of the amplifiers and its other terminal connected to a common output terminal, and means for biasing the rectifiers so that, in use, the random noise signals from the amplifiers are combined at the common output terminal to produce a resultant noise signal having an amplitude less than those of the individual noise signals, each of the amplifiers of the circuit being arranged to receive as an input the electrical signal generated by one or more of the photosensitive devices.
 2. Apparatus as claimed in claim 1, in which the inspection head comprises a housing on which are mounted a plurality of the photo-sensitive devices and a separately formed, replaceable collimating member having an aperture through which, in operation, light transmitted through or reflected from the sheet passes, to fall onto the photo-sensitive devices, the collimating member being detachably fixed to the housing.
 3. Apparatus as claimed in claim 2, in which the inspection head comprises a plurality of housings formed by a corresponding number of separate head sections, each head section being detachably mounted on a common support member extending transversely of the direction of flow of sheet material through the apparatus.
 4. Apparatus as claimed in claim 3, in which the support member is hinged to a main frame of the apparatus, to enable the inspection head to be moved from an operative position in which the aperture of each collimating member is close to the path of travel of sheet material.
 5. Apparatus as claimed in claim 2, in which the or each housing is in the form of an airtight case, and means are provided for supplying dust-free air under pressure to the housing, the air leaving the housing through the apertures in the collimating members.
 6. Apparatus as claimed in claim 1, in which adjustment means are provided for adjusting the distance between the apertures of the collimating members and the path of travel of the sheet material.
 7. Apparatus as claimed in claim 1, in which there are provided support means providing a support surface for supporting sheet material as it passes the inspection head, the support means being adjustable to enable the support surface to be made selectively convex, flat or concave.
 8. Apparatus as claimed in claim 2, in which the or each collimating member comprises two side walls converging towards the path of the sheet material, the aperture being defined beTween flat faces formed at adjacent ends of the side walls and parallel to the plane of symmetry of the collimating member.
 9. Apparatus as claimed in claim 8, in which the or each collimating member is divided by ribs extending between the side walls into sections each corresponding to one of the photo-sensitive devices.
 10. Apparatus as claimed in claim 2, in which the or each collimating member comprises two side walls converging towards the path of the sheet material, the adjacent ends of the side walls being cut off in a plane parallel to the plane of movement of the sheet past the members, the aperture being defined by the adjacent edges of the inner surfaces of the side walls.
 11. Apparatus as claimed in claim 2, in which the or each collimating member comprises a slit of adjustable width positioned between the photo-sensitive devices and the path of sheet material, and the light source means comprises lamps positioned at a comparatively large distance from the path of the sheet at the side of the path remote from the photo-sensitive devices, so that substantially parallel beams of light transmitted through sheet material in the path pass through the slit onto the photo-sensitive devices.
 12. Apparatus as claimed in claim 2, in which the or each collimating member includes fibre-optics means arranged to conduct light reflected or transmitted from the sheet material to the photo-sensitive devices.
 13. Apparatus as claimed in claim 12, in which fibre-optics means is provided to conduct light from the light source means to the sheet material.
 14. Apparatus as claimed in claim 1, in which the photo-sensitive devices are adapted to respond to infrared radiation, and infrared filters are disposed between the light source means and the sheet material.
 15. Apparatus as claimed in claim 1, in which the or each collimating member includes an aperture adapted to be oscillated in a direction transverse to the path of sheet material and parallel to the plane of the sheet as it passes the apertures, to detect line defects of the sheet extending in the direction of flow of the sheet. 